The invention pertains to condensate draining, air pressure sealing valves that are mounted on an aircraft fuselage at various positions along the belly to drain off condensate collected in the bilge-like area of the fuselage, and to close in response to cabin air pressurization to form an airtight seal.
Because of the water draining purpose of these valves and their placement on the belly of the aircraft fuselage, they are sometimes referred to in the industry as "bilge valves." A number of bilge valve configurations have been heretofore proposed, and for large, commercial carrier aircraft, a widely-used, self-acting valve mechanism comprises an inverted U-shaped metal bracket supporting a spring baised flapper valve preassembled as a unit and permanently installed on the inside surface of the fuselage wall with the flapper in registration with a drain opening in the fuselage wall. The flapper is normally biased away from the opening for condensate drainage, and closes in response to increasing differential air pressure due to cabin pressurization.
While such flapper-type bilge valves work fairly well when the aircraft is new, and under ideal conditions of a clean, debris-free bilge area, aging of the aircraft, and, a normal accumulation of dirt, grit, metal chips, and dropped fastener parts, such as nuts, bolts, rivots, etc., results in such debris being carried by draining water and escaping air to the valve mechanism and where it often interferes with the proper opening and closing of the flapper valve. The valve may be stuck in the closed position or partially closed position preventing proper drainage of condensate which will lead to rust and deterioration of the fuselage wall. A valve stuck in the open or partially opened position allows air to escape through the valve during cabin pressurization and results in consequence loss of air conditioning efficiency. Currently, the relatively small loss of air through a malfunctioning bilge valve is tolerated and compensated by simply increasing the source of fresh, cabin pressurizing air from the bleed-air system of the engines. However, recent efforts to design more efficient aircraft systems have placed limitations on the amount of available bleed-air and this in turn has demanded greater efforts to seal off the fuselage interior during cabin pressurization to minimize air loss. Furthermore, safety requirements sometimes demand an airtight seal during cabin pressurization so that in the event of a fire, fire extinguishing chemicals, which are automatically discharged into the cargo compartments, are not dissipated by escaping through incompletely closed bilge valves. Another disadvantage of leaking bilge valves is that the escaping air, being at a lower velocity than outside airstream, causes turbulance which in turn produces undesirable drag. Conventional flapper valves of the above-described type, have not always provided the needed airtight seal, mostly because of interference from the inevitable debris that accumulates in the aircraft bilge area. Also, the flapper type valves are notoriously difficult to install and are often located in misalignment with the drain opening thereby decreasing the effectiveness of the air seal when the valve is closed.
Furthermore, in order to correct a bilge valve that has malfunctioned for one or more of the above reasons, it is necessary to replace the valve by gaining access to the interior belly of the fuselage, which in most modern, commercial carriers requires the removal of the cargo floorboards over the location of each of the bilge valves. A typically large jet powered commercial carrier may have as many as thirty to forty of these bilge valves placed at various locations along the length of the fuselage, requiring a major servicing effort to first gain access to the belly area where the valve is mounted and then removing the valve and installing a new one. Because of the difficulty in servicing these valves, often aircraft owners will simply accept the costly loss of cabin air and the consequent inefficiency of the bleed-air system and increased fuel consumption.
While other valve configurations have been proposed, such proposals either do not solve one or more of the above noted primary problems, or the designs are impractical because of being too costly to manufacture and/or to maintain, too fragile for long trouble-free operation (for example some existing bilge valves are susceptible to being crushed by workmen walking on the fuselage wall during assembly and maintenance of the aircraft), too heavy, too susceptible to corrosion, and create undesirable resistance to airflow due to excessive projection from the exterior surface of the fuselage wall.